This invention relates to a heat treating device for safely and efficiently heat-treating product to be treated at relatively low temperature such as below 100.degree. C., using reduced pressure steam and/or water as heat media.
In the field of chemical industry and food industry, materials may be treated at relatively low temperature such as about 50.degree. C. for example for the purpose of safety of working and maintenance of product quality. Such a reduced pressure steam heat treating device as disclosed in the Japanese opened patent gazette No. H1l-315336 has been proposed for this heat treatment. As shown in FIG. 1, this device includes a reaction vessel 1 for causing materials supplied from an inlet 5 to react as stirring them by a stirrer 7 and delivering reaction product from an outlet 9, a heat exchanger 11 of jacket type having an inlet 13 and an outlet 15 of a heat media such as steam and water and surrounding the vessel 1, a piping 17 for feeding heating steam to the heat exchanger 11 through an automatic valve 19, a suction pump 21 of ejector type having its suction port 23 connected to the outlet 15 of the heat exchanger 11 through a piping 24, a water tank 25 having a diffuser 27 of the ejector 21 connected to its upper space and being provided with level sensors 29a and 29b and a temperature sensor 31, a piping 33 for feeding cooling water to the water tank 25 through an automatic valve 35, a piping 37 for connecting a lower portion of the tank 25 to a jetting nozzle 41 of the ejector 21 through a pump 39, a piping 43 for connecting the piping 37 to the inlet 13 of the heat exchanger 11 through an automatic valve 45, a draining piping 47 for connecting the piping 43 to the exterior through an automatic valve 49, and a central control unit 51 for receiving signals from the sensors 29a and 29b and 31 to control the respective automatic valves. When the pump 39 is driven, the water in the tank 25 circulates through the piping 37 and the ejector 21 to maintain the ejector 21 in a sucking state.
When the reaction vessel 1 is heated, the valve 19 is opened and the valve 45 is closed by a signal from the central control unit 51, and heating steam is supplied from the piping 17 to the heat exchanger 11. The steam is sucked by the ejector 21 to enter the water tank 25 together with condensed water, thereby raising the water temperature within the tank 25 gradually. Since the interior of the heat exchanger 11 is put in a reduced pressure state by the ejector 21, saturation temperature of the steam is low and the materials can be caused to react at a temperature below 100.degree. C. In the case of turning from heating to cooling, the valve 19 is closed and the valve 45 is opened by a signal from the central control unit 51, and cool water is supplied into the tank 25, thereby lowering the water temperature within the tank 25 gradually. Thus, the reaction vessel 1 cooled with water whose temperature lowers gradually. The water temperature within the tank 25 is sensed by the temperature sensor 31 and the central control unit 51 responds thereto to control the valve 35, thereby controlling a change of the water temperature in accordance with a predetermined program to control a temperature change of the heat exchanger 11. The level sensors 29a and 29b sense the upper and lower limit of the water level, respectively, and the central control unit 51 responds thereto to control the valves 35 and 49 for maintaining the water level of the tank 25 substantially constant.
In this prior art device, the temperature difference between the initial cooling water and the heating steam is small at the time of turning from heating to cooling and, therefore, it has such an advantage in that there is no hammering effect caused by thermal shock and a lifetime of the device can be extended.
However, problem exists in that, although the reduced pressure level within the heat exchanger 11 must be precisely controlled for effecting a predetermined temperature control of the heat exchanger 11, water having condensed from the steam within the heat exchanger 11 at the time of heating or remaining therein from evaporation at the time of cooling may pool in the vicinity of the outlet 15 to clog it up, thereby causing variation in the reduced pressure level and, accordingly, in the temperature, which results in variation in the quality of the reaction product. Moreover, it is also a problem in that the water pooling in the vicinity of the outlet 15 actually makes it impossible to lower the heating temperature below 50.degree. C. since it impedes pressure reduction within the heat exchanger 11. Consideration has been given to a branch the piping 24 connect to the upper portion of the heat exchanger 11 for promoting reduction of the pressure, but no actual pressure reducing effect would be gained since the condensed water is sucked preferentially. On the other hand, to control supply of the steam and water so as to prevent the water from pooling is undesirable since it needs a very complicated and expensive control device.
Accordingly, an object of this invention is to provide an improved device which can effect an effective heat treatment at a much lower temperature regardless of the above-mentioned water pooling, by adding a simple improvement to the above-mentioned prior art device.